Annealed wafer manufacturing method and annealed wafer

Abstract

The present invention provides an annealed wafer manufacturing method using a heat treatment method causing no change in resistivity of a wafer surface even when a silicon wafer having boron deposited on a surface thereof from an environment is subjected to heat treatment in an insert gas atmosphere and enabling the heat treatment in an ordinary diffusion furnace not requiring a sealed structure for increasing airtightness nor any specific facility such as explosion-proof facility. The present invention also provides an annealed wafer in which a boron concentration in the vicinity of a surface thereof is constant and crystal defects are annihilated. In the annealed wafer manufacturing method, a silicon wafer having a natural oxide film formed on a surface thereof with boron deposited thereon from an environment is subjected to heat treatment in an atmosphere containing hydrogen gas to remove the deposited boron before the natural oxide film is removed, and then is subjected to heat treatment in an inert gas atmosphere.

Description

TECHNICAL FIELD[0002]The present invention relates to an annealed wafer manufacturing method enabling suppression of a change in resistivity due to an increase in a boron concentration in the vicinity of a surface of a wafer which is annealed in an atmosphere of 100% inert gases such as argon, and to a high quality annealed wafer manufactured by the manufacturing method having a constant boron concentration in the vicinity of the wafer surface with crystal defects being annihilated.BACKGROUND ART[0003]A silicon wafer (hereinafter may be simply referred to as a “wafer”) is required to have no crystal defects in an active layer of a device from the viewpoint of device characteristics. To satisfy this requirement, there has been used an annealed wafer manufactured by annealing a wafer at a high temperature to reduce crystal defects. The wafer is, however, apt to be easily contaminated by boron present in an environment (in peripheral air) to which the silicon wafer is exposed. For inst...

AI Technical Summary

Benefits of technology

[0016]As described later, boron deposited on a surface of a wafer from an environment hardly diffuses into the wafer when a natural oxide film is present on the wafer surface. Therefore, when the second heat treatment is performed after the deposited boron is removed by making use of the effect by hydrogen gas in the state where the natural oxide film is present, it is possible to prevent a resistivity change in the vicinity of the wafer surface due to the second heat treatment. In this case, if the hydrogen gas concentration in the first heat treatment is equal to or lower than a lower explosion limit thereof (about 4%), the sealed structure for increasing airtightness in a heat treatment furnace or an explosion-proof facility as a measure at the time of the explosion is not required, and an atmospheric pressure furnace can be used, which is advantageous in safety as well as cost. It should be noted that the sufficient effect may not be expected when the hydrogen concentration is less than 0.1%.

[0024]Then the present inventors carried out the experiments described below to confirm whether it is possible or not to remove the deposited boron by using argon gas atmosphere containing hydrogen gas of a concentration equal to or lower than the lower explosion limit thereof as a heat treatment atmosphere for removing the deposited boron. As a result, the present inventors newly discovered the phenomenon that, only when a heat treatment temperature in the argon gas atmosphere containing the hydrogen gas of a concentration equal to or lower than the lower explosion limit thereof is set to a specific temperature range as shown in FIG. 4 (the temperature range of 900 to 1100° C., and preferably 950 to 1050° C. as shown in FIG. 4), the resistivity of the original wafer is maintained.

[0029]In the experiment described below as an example, even when the first heat treatment was performed in the temperature range of 950 to 1050° C., resistivity of the silicon wafer did not change, and at the temperatures of 900° C. or 1100° C., the resistivity changed only a little, and therefore it can be considered that, when the first heat treatment is performed in the temperature range of 900 to 1100° C., a resistivity change of a wafer can be prevented by adjusting the heat treatment time in the range of the order of 5 to 60 minutes.

Problems solved by technology

The wafer is, however, apt to be easily contaminated by boron present in an environment (in peripheral air) to which the silicon wafer is exposed.

As a measure against boron present in an environment of a clean room, sometimes boron absorption filters or boronless filters are used for all air filters in the clean room, but it is necessary to frequently exchange the expensive filters with new ones, which results in a cost increase, and in addition even use of the filters as described above can not eliminate boron contamination completely.

On the other hand, when annealing is performed with hydrogen, boron dopant originally present inside the wafer easily outdiffuses, and further boron deposited on the surface evaporates or flies without diffusing into the wafer even by annealing, so that the boron concentration in the vicinity of the wafer surface decreases with the resistivity becoming problematically higher.

To perform hydrogen treatment at a high temperature, a safeguard or the like is required to prevent explosion of hydrogen, which may raise such problems as a cost increase and a productivity decrease.

Although this method is extremely useful from the viewpoint of prevention of boron contamination, there is a problem with the method from the viewpoint of deposition of particles.

Namely even if the final cleaning is performed with diluted hydrofluoric acid and then the wafer is cleaned with water, particles deposited in the diluted hydrofluoric acid are hardly cleaned down, and are carried up to the annealing step, so that, when the wafer is annealed, baking of the particles takes place to possibly cause a yield drop in fabrication of devices.

Therefore, if it is tried to carry out the processing using an ordinary diffusion furnace, a safeguard for using hydrogen and facilities for performing the processing in a depressurized state are required, and therefore the method cannot be applied in a furnace not equipped with such facilities.

When the resistivity of the wafer surface changes, in the case of, for instance, a MOS device, the on-off threshold voltage changes, which may not meet standard requirements.

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